VLC media player is the most stable, flexible and lightweight audio and video player around today, especially when compared to others that will play unusual formats after downloading a codec, or simply refuse to play things.

The program handles tons of formats, from MPEG to FLV and RMBV files. V10 bit codes plus multi-threaded decoding for H.264, MPEG-4/Xvid and WebM, as well as the ability to play HD and BluRay. Also useful is the fact that you can use VLC media player to preview files you are downloading since it plays incomplete parts of video files. VLC media player is not just for video playback however.